MagneSensors' Phase I SBIR uses magnetic sensors and magnetic nanoparticle labels in new ultra-sensitive sandwich immunoassays. The focus is on measuring very low levels of antigens in blood using the highly desirable mix and measure format. This combination is extremely difficult to achieve and is currently not available in competing bioassay platforms. Magnetic detection offers unique advantages, such as the quantitative measurement of binding without requiring the usual separation of unbound labels, as well as the inherent lack of magnetic background in blood and serum. This magnetic detection platform uses high temperature superconducting quantum interference devices (SQUIDs) to detect the specific binding to antigens of antibodies labeled with magnetic nanoparticles. Importantly, the ultra-high levels of sensitivity for sandwich immunoassays will take advantage of our new, next-generation magnetic detection instrument that will be brought on line shortly under a separate NIH program. This new bench top instrument uses a small cryorefrigerator and offers 50-200X better signal-to-noise than our existing instrument along with much higher throughput. High sensitivity offers advantages of early detection and measurements on small volumes of valuable reagents or scarce samples. The mix and measure format significantly reduces assay preparation time and simplifies automation (no wash steps), thereby enabling rapid, high throughput assays. The ability to work in blood and serum brings these benefits to a much broader range of important immunoassays. The Phase I aim is to demonstrate ultra high sensitivity magnetic sandwich immunoassays on an interleukin-6 (IL-6) model system with the following goals: 1) whole blood, 2) <0.4 pg/ml, 3) no separation of unbound magnetic nanoparticle labels, 4) <60 minutes total assay time including preparation and measurement. Phase I focuses on detection of an antigen in blood using a sandwich magnetic immunoassay format. The detection goal of 0.4 pg/ml is at the lower end of endogenous levels of IL-6 in blood. It will be achieved in Phase I using a novel technique we have developed that uses silica microbeads and a density gradient media to remove the captured antigen from blood cells prior to magnetic detection. Note that the Phase I effort does not develop a true mix and measure immunoassay in blood, as blood cells are separated out from captured antigen in Phase I. This more ambitious goal, currently unachievable at ultra-high sensitivity with other detection platforms, is left for Phase II. [unreadable] [unreadable] [unreadable]